1. Field of the Invention
The present invention relates to a mobile communication terminal. More particularly, embodiments of the present invention are directed to methods for searching a network using a mobile communication terminal.
2. Discussion of the Related Art
Typically, a mobile communication terminal, such as a wireless telephone or personal digital assistant (PDA) telephone, must recognize a base station network in order to communicate with another base station. FIG. 1 illustrates one example of a general process for controlling a mobile communication terminal to recognize a base station network.
When the mobile communication terminal is powered on, the mobile communication terminal searches for a physical channel in an order of descending power levels in order to detect a Frequency Burst (FB) to carry out frequency synchronization at step S1. If the mobile communication terminal detects the FB at S1, the mobile communication terminal then detects a synchronization burst (SB) channel to be synchronized with the FB at S2. The mobile communication terminal next reads system data and cell data, and extracts network information specific to the physical location where the mobile communication terminal is currently located. This is denoted at S3. Thereafter, the mobile communication terminal performs registration at S4, and is then switched to an idle mode at step S5.
Typically, when a mobile communication terminal equipped with a temperature compensation crystal oscillator (TCXO) scans a signal channel to search for a frequency burst channel, the mobile communication terminal uses a fixed automatic frequency correct (AFC) value stored in a memory location. The mobile communication terminal generally searches for the signal channel a total of four times, such that a maximum search time of about 30 seconds elapses.
In contrast to a TCXO, a digitally controlled crystal oscillator (DCXO) is not equipped with a temperature compensation function. When a mobile communication terminal employing a DCXO scans a signal channel to search for a frequency burst channel, the mobile communication terminal generally searches the signal channel a total of 12 times using various AFC (Automatic Frequency Correct) values. In more detail, the mobile communication terminal searches the signal channel using a first AFC value (AFCCENTER) four times, searches using a second AFC value (AFCMAX) four times, and searches using a third AFC value (AFCMIN) four times.
FIG. 2 discloses an example of a conventional network search method. If a code signal represents a network search request at S101, a mobile communication terminal selects one of the channels contained in a channel list at S102. The mobile communication terminal then sets an AFC value to a specific value of AFCCENTER at S103, and searches for the network until detecting a frequency burst (FB) at most four times at S104, S105, and S106.
If the mobile communication terminal falls to detect the FB after searching four times, it changes the AFC value to AFCMAX at S107, and searches for the FB four times at s S108, S109, and S110. If the mobile communication terminal fails to detect the FB while searching for the FB four times using AFCMAX as the AFC value, it changes the AFC value to AFCMIN at S111, and searches for the FB four times at S112, S113, and S114.
If the mobile communication terminal applies all the values of AFCCENTER, AFCMAX, and AFCMIN to a signal channel, and fails to detect the FB after searching for the FB four times using each of the values AFCCENTER, AFCMAX, and AFCMIN, the mobile communication terminal transmits a search failure message at S115, changes the current channel to another channel at S116, and returns to the frequency search routines S102-S114.
Alternatively, if the mobile communication terminal successfully detects the FB, it searches for a synchronization burst (SB) channel to be synchronized with the FB at S119. If the mobile communication terminal successfully detects the SB channel, it is switched to an idle mode at S120. If the mobile communication terminal fails to detect the SB channel, it changes a current channel to another channel at S116, and returns to the frequency search routines S102-S114.
If the mobile communication terminal fails to detect the frequency burst (FB) after searching through all of the channels contained in the channel list, it generates a network lost signal.
If a code signal at S101 does not represent a network search request, the mobile communication terminal checks for a network lost signal. If the mobile communication terminal detects a network lost signal at S117, the mobile communication terminal executes a temperature compensation process to compensate for an incorrect oscillator frequency caused by heat encountered during the frequency search method at S118.
As described above, the mobile communication terminal equipped with the DCXO searches for a FB associated with a signal channel a total of 12 times (i.e., AFCCENTER (4 times), AFCMAX (4 times), or AFCMIN (4 times)). As a result, a total search time consumed from a “No Service” state to a specific time at which the mobile communication terminal re-performs the network search method is about 1 minute and 30 seconds, which is a relatively long network search time. Therefore, although including a DCXO with a mobile communication terminal reduces the cost of production of the mobile communication terminal, this also results in users of the mobile communication terminal experiencing greater inconvenience due to long network search times.